Depending on the context of the business, it could also mean exploring new product categories, like a bicycle maker deciding to get into the skateboard market because it happens to be popular. Or in the context of an online news website, a "vertical" is whether you are writing about tech, or health, or pop culture, etc...

When I wrote for MUO (very briefly) I was assigned to the creative software "vertical"; writing articles about video editing software, updates to different paint/art programs, etc...